Polymer encapsulated micro-thermocouple

ABSTRACT

A catheter comprising a catheter sleeve and a micro-thermocouple adapted to move within the sleeve, wherein the micro-thermocouple includes a first insulated conductor, wherein the first conductor has a diameter ranging from around 0.00009 inches to 0.005 inches, a second insulated conductor, and a coupled region including a bare region of the first insulated conductor coupled to a bare region of the second insulated conductor and an electrically insulative cover.

RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 12/077,316, filed Mar. 17, 2008, the specification of which isincorporated herein by reference in its entirety, which is acontinuation of U.S. patent application Ser. No. 10/391,531, filed Mar.17, 2003, and issued Apr. 22, 2008 as U.S. Pat. No. 7,361,830, thespecification of which is incorporated herein by reference in itsentirety.

Pursuant to 35 U.S.C. § 119(e), this patent application claims thebenefit of related U.S. Provisional Application No. 60/366,435 filedMar. 21, 2002, which is hereby incorporated by reference in itsentirety.

TECHNICAL FIELD

This patent application relates to thermocouple devices, and inparticular, to a thermocouple device produced by encapsulating athermocouple junction with a heat-shrinkable polymer coating.

BACKGROUND

A thermocouple is a bimetal junction that provides a voltageproportional to temperature. Temperature probes are often formed usingthermocouples. Many applications requiring temperature probes requireextremely small size.

One application for extremely small temperature probes is in the medicaldevice industry; especially for use in catheters. For example, ablationcatheters are used in non-invasive treatment of heart abnormalities. Theablation catheter is able to identify abnormal tissue growth and usesheat to remove the tissue causing the additional conduction paths.Thermal feedback is required when removing the tissue to prevent bloodclotting or blood boiling during the procedure. In using a temperatureprobe to provide this feedback, the probe must be small enough to get asnear an ablation electrode as possible. Also, when used in catheters, itis desirable that a temperature probe not rupture a catheter sleeve bytearing or abrasion. Further, a probe should be electrically insulatedto allow in vivo operation.

It is apparent that uses for extremely small temperature probes beyondthe medical field are possible. An extremely small probe would be usefulin any field where a measurement of a localized temperature variation isdesired, such as for example, the field of electronics.

What is needed is an insulated thermocouple device of extremely smallsize.

SUMMARY

This document discusses a catheter with an insulated micro-thermocoupledevice of extremely small size. The catheter comprises a catheter sleeveand the micro-thermocouple adapted to move within the sleeve, whereinthe micro-thermocouple includes a first insulated conductor having adiameter ranging from around 0.00009 inches to 0.005 inches, a secondinsulated conductor, and a coupled region including a bare region of thefirst insulated conductor coupled to a bare region of the secondinsulated conductor and an electrically insulative cover.

This summary is intended to provide an overview of the subject matter ofthe present application. It is not intended to provide an exclusive orexhaustive explanation of the invention. The detailed description isincluded to provide further information about the subject matter of thepreset patent application.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings like numerals refer to like components throughout theseveral views.

FIG. 1 is a drawing of one embodiment of the micro-thermocouple.

FIG. 2 is a flowchart showing one method for forming themicro-thermocouple.

FIG. 3 is a drawing of showing fused embodiments of themicro-thermocouple.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof, and specific embodimentsin which the invention may be practiced are shown by way ofillustration. It is to be understood that other embodiments may be usedand structural changes may be made without departing from the scope ofthe present invention.

As stated previously, the present application is concerned withmaterials and techniques used to create a sealed thermocouple ofextremely small size. FIG. 1 shows one embodiment of amicro-thermocouple 100. The thermocouple junction 130 is formed fromjoining conductors 120, 122 of dissimilar metals. The metals compriseany of the standard metal combinations defined by the American Societyof Testing and Materials (A.S.T.M.) for thermocouples. The size of thethermocouple conductors generally fall with a range of about 30 awg(0.010 inch diameter) to about 50 awg (0.0009 inch diameter). In oneembodiment conductors 120, 122 are joined to form a thermocouplejunction 130 by soldering using lead-free solder 135. In anotherembodiment, conductors 120, 122 are welded and 135 represents a weldedbead or seam. Beyond the thermocouple junction 130, the conductors 120,122 are electrically insulated with commonly used insulating material140 such as nylon, polyurethane, or polyimide. A heat shrinkable polymermaterial is then used to form an electrically insulating seal 150 overthe micro-thermocouple 100. To create the seal 150, a tube is slid overthe thermocouple junction. In one embodiment, the tube is slid over thethermocouple junction and the seal 150 is then formed by heating thetube of polymer material to the point of melting onto and over thethermocouple joint 130 and onto the insulation 140. Melting the polymermaterial onto the thermocouple conductor insulation 140 provides a sealaround the insulation 140. The melting also forms a domed shape 155 onthe end of micro-thermocouple 100. This domed end 155 is advantageous ifthe thermocouple is used in a catheter as it results in themicro-thermocouple 100 being resistant to abrading or tearing a cathetersleeve. In another embodiment, the tube of heat shrinkable polymermaterial is first sealed on one end by melting the end and forming thedomed end before the tube is slid over the thermocouple junction. Afterthe tube is slid over the thermocouple junction 130, further heating andmelting provides the insulating seal 150. Other embodiments involvesealing the end while it is placed over the thermocouple junction 130.

The length (l) 160 of the resultant seal 150 is within the range ofabout 0.05 inches to 0.5 inches. The overall length (L) 165 of themicro-thermocouple 100 is within the range of about 20 inches to 78inches. One embodiment of the micro-thermocouple 100 uses polyethyleneterephthalate (PET) as the polymer material. Another embodiment usesfluorinated ethylene propylene (FEP). The seal 150 is moisture resistantand electrically insulating. The insulation resistance of the seal isgreater than 100 Mega-ohms when measured at 50 Volts (DC).

FIG. 1 also shows a cross section 110 of micro-thermocouple 100. Thewidth (w) 170 of the micro-thermocouple 100 falls within a range fromabout 0.005 inches to 0.011 inches. The height (h) 175 of themicro-thermocouple 100 falls within a range of about 0.003 inches to0.01 inches. Thus, it can be seen that the micro-thermocouple can beformed within a reproducible confined shape having a height 175 lessthan about 0.01 inches and a width 170 less than about 0.011 inches. Thefinal dimensions of the confined shape are determined in part by thegauge of the thermocouple conductors used. Providing the insulation bythe technique described herein adds about 0.0005 inches to the width andheight dimensions of a formed thermocouple junction.

FIG. 2 shows a flowchart of one embodiment of a method 200 of formingmicro-thermocouple 100. At 210, insulation 140 is removed from a distalend of thermocouple conductors 120, 122. At 220, a thermocouple junction130 is formed at the distal end of the conductors 120, 122. At 230, thetube of polymer material is slid over the thermocouple junction 130. At240, a seal 150 is formed over the thermocouple junction 130 by heatingand melting the polymer material.

FIG. 3 shows fused embodiments of the micro-thermocouple 100. A fusedthermocouple prevents the possibility of recycling or reusing thethermocouple if the micro-thermocouple 100 is used in a medical device.In one embodiment a fuse 390 is placed in a thermocouple conductor 120between a proximal end of the conductor 120 and the thermocouple joint130. Exceeding the rating of the fuse breaks the electrical connectionbetween the proximal end of conductor 120 and the thermocouple joint. Inanother embodiment, a fuse 395 is formed by placing within thethermocouple junction 130. Exceeding the rating of the fuse 395 acrossthe thermocouple conductors 120 causes the device to lose the propertiesof a thermocouple.

Although specific examples have been illustrated and described herein,it will be appreciated by those of ordinary skill in the art that anyarrangement calculated to achieve the same purpose could be substitutedfor the specific example shown. This application is intended to coverany adaptations or variations of the present invention. Therefore, it isintended that this invention be limited only by the claims and theequivalents shown.

1. An catheter, comprising: a catheter sleeve; and a micro-thermocoupleadapted to move within the sleeve, wherein the micro-thermocoupleincludes: a first insulated conductor, wherein the first conductor has adiameter ranging from around 0.00009 inches to 0.005 inches, a secondinsulated conductor, and a coupled region including a bare region of thefirst conductor coupled to a bare region of the second conductor and anelectrically insulative cover.
 2. The catheter of claim 1, wherein thesecond conductor has a diameter ranging from around 0.00009 inches to0.005 inches
 3. The catheter of claim 2, wherein the insulative coverincludes a dome shape end for protecting the catheter sleeve when themicro-thermocouple moves within the sleeve.
 4. The catheter of claim 2,wherein the insulative cover includes fluorinated ethylene propylene. 5.The catheter of claim 2, wherein the coupled region has a junctionheight and a junction width, and the insulative cover has a height lessthan 0.0005 inches greater than the junction height and width less than0.0005 inches greater than the junction width.
 6. The catheter of claim2, wherein the thermocouple conductors are conductors of types selectedfrom a set of A.S.T.M. types T, J, K, E, S, R, and B.
 7. The catheter ofclaim 2, wherein the junction further comprises a fuse.
 8. The catheterof claim 7, wherein the fuse located between a proximal end of at leastone of the thermocouple conductors and the thermocouple junction, suchthat exceeding an electrical rating of the fuse breaks an electricalconnection between the proximal end of the conductor and thethermocouple junction.
 9. The catheter of claim 2, wherein soldercouples the first and second thermocouple conductors along a length ofthe coupled region.
 10. The catheter of claim 2, wherein the coupledregion has a width ranging from around 0.005 inches to around 0.011inches.
 11. The catheter of claim 10, wherein the coupled region has aheight ranging from around 0.003 inches to around 0.01 inches.
 12. Thecatheter of claim 2, wherein the insulative cover includes polyethyleneterephthalate.